Mucopolysaccharidosis type IVA (MPSIVA; Morquio A disease: OMIM #253000) is an autosomal recessive Lysosomal Storage Disorder (LSD) caused by the deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS, EC 3.1.6.4). The gene discussed is GALNS; the disease is mucopolysaccharidosis type 4A.